This invention relates to a sliding bearing, particularly to a sliding bearing in which a bearing metal layer is covered with a coating layer.
Sliding bearings in which a layer of a bearing metal such as copper alloy, aluminum alloy or the like is covered with a coating layer comprising a resin as the base are disclosed in, for example, JP-A 58(1983)-108,299. In this publication, the coating layer to be applied to the layer of a bearing metal such as aluminum alloy or the like is formed by incorporating a solid lubricant such as graphite, molybdenum disulfide or the like into a thermosetting resin such as a phenolic resin, an epoxy resin or the like, with the intention of improving the anti-seizure property of the coating layer.
Moreover, JP-A 4(1992)-83,914 discloses an improvement of the lubricity of the coating layer by adding a polyimide resin as a binding material to a solid lubricant such as molybdenum disulfide or the like. Furthermore, an example is shown in which hard particles such as chromium oxide particles, aluminum oxide particles or the like are added to improve the wear resistance.
In addition, JP-A 10(1998)-37,962 describes that the wear resistance is improved by allowing the: hard particles added to the resin and the solid lubricant having a spherical shape.
Recently owing to the high power and high revolution speed of internal combustion engine, the sliding bearings have become used under severer conditions, so that sliding bearings having a higher quality have been desired.
As shown in the above-mentioned conventional techniques, in the case of the coating layer in which a solid lubricant is added to a thermosetting resin used as the base resin, the coefficient of friction has been improved, but the wear resistance has rather become low. Further, in the case of the coating layer in which hard particles are added to the thermosetting resin, wear resistance has been improved, but anti-seizure property have become low. Thus, it has been impossible to make the coating layer excellent in all of coefficient of friction, wear resistance and anti-seizure property which are required for sliding bearings, so that sliding bearings in which a balance has been maintained among these properties have been prepared. Moreover, there has been a limit in improving these properties by only controlling the composition of the solid lubricant and the hard particles.